1. Field of the Invention
This invention relates to an electrophotographic printer, and more particularly to an electrophotographic printer of the type wherein a toner powder image electrostatically adhering to a photosensitive member is transferred to paper to effect desired printing.
2. Description of the Prior Art
Various electrophotographic printers are known. An exemplary one of conventional electrophotographic printers is shown in FIG. 7. Referring to FIG. 7, a cylindrical photosensitive member 1 is disposed for rotation in the inside of a printer body not shown. A toner unit 3 having a substantially L-shaped cross section is disposed adjacent an outer periphery of the photosensitive member 1 such that the opposite ends thereof are positioned in the proximity of the outer peripheral face of the photosensitive member 1, and toner powder 2 is accommodated in the photosensitive member 1. A charger 4 for applying charge uniformly to a surface of the photosensitive member 1 by corona discharge to put the photosensitive member 1 into a write-enabled condition and an LED (light emitting diode) head 5 serving as an optical writing head for forming an electrostatic latent image on the semiconductor layer 1 in response to a printing signal are disposed in this order between the photosensitive member 1 and the toner unit 3. A developing roll 6 for applying toner power 2 of the toner unit 3 to an electrostatic latent image written by the LED head 5 to form a visible toner image is disposed in the toner unit 3 on the downstream side of the LED head 5 in the direction of rotation of the photosensitive member 1. A cleaning blade 7 for removing remaining toner powder 2 sticking to the surface of the photosensitive member 1 and recovering it into the toner unit 3 is disposed in the toner unit 3 on the upstream side of the charger 4 in the direction of rotation of the photosensitive member 1. A plurality of transport paddles 8 for feeding toner power 2 accommodated in the toner unit 3 toward the developing roll 6 is disposed in the toner unit 3.
transfer unit 10 in the form of a corona discharger for transferring a visible toner image developed by the developing roll 6 to a predetermined paper sheet 9 is disposed adjacent the photosensitive member 1 between the developing roll 6 and the cleaning blade 7.
In the conventional electrophotographic printer described above, the photosensitive member 1 is first put into a write-enabled condition by the charger 4, and then an electrostatic latent image is formed on the photosensitive member 1 in response to a printing signal by the LED head 5. Then, toner powder 2 accommodated in the toner unit 3 and fed by the transport paddles 8 is supplied to the photosensitive member 1 so that it may adhere to the electrostatic latent image formed on the photosensitive member 1 to form a visible toner image. After then, the toner image is transferred by the transfer unit 10 to a paper sheet 9 which is transported between the photosensitive member 1 and the transfer unit 10. After then, the paper sheet 9 is exfoliated from the photosensitive member 1, and the toner image is fixed to the paper sheet 9 by a fixing unit not shown, thereby completing desired printing.
Meanwhile, remaining toner powder 2 on the photosensitive member 1 is removed by the cleaning blade 7 to put the photosensitive member 1 into a chargeable condition again, and the toner powder 2 removed from the cleaning blade 7 is recovered into the toner unit 3, in which it is thereafter stored for the re-utilization.
In the conventional electrophotographic printer, however, the charger 4 and the LED head 5 must be disposed between the developing roll 6 and the cleaning blade 7 which are both disposed in the toner unit 3, and to this end, the toner unit 3 must necessarily be shaped such that it extends over the rear sides of the charger 4 and the LED head 5. Consequently, the toner unit 3 generally has a great overall size. Besides, the removing or mounting direction of the toner unit 3 upon replacement is limited by the charger 4 and/or the LED head 5, which provides a very limited degree of freedom in designing.
Moreover, since the toner unit 3 has such a profile that it extends over the rear sides of the charger 4 and the LED head 5, ozone gas generated from the charger 4 and heat generated from the LED head 5 are confined between the toner unit 3 and the photosensitive member 1, which deteriorates the photosensitive member 1 remarkably and gives rise to reduction in life of the photosensitive member 1. In addition, since the gap between the toner unit 3 and the photosensitive member 1 is small, cleaning of the surfaces of the charger 4 and the LED head 5 is very difficult.